Largely concur, but keep in mind if you are moving to spray fluxing to
get benefits of low solids for no clean then it is better to monitor
the flux activity directly rather than inferring it by measuring SG
and assuming that this relates directly to solids content and
therefore flux activity arising from solids. Your flux suppler will
have kits for doing this.
The reason: SG is affected by more than just dissolved solids. At high
dissolved amounts these other things probably don't matter too much.
At very low solids contents the variations in SG caused by things like
ambient temperature (cold things contract and are therefore denser
than hot things) and by water absorption (SG water is 1, alcohol is
around 0.8) are as significant as that caused by solids content.
Clearly if water does become absorbed the SG will rise although the
solids content is
actually same or reduced - error is increased if you then correct SG
with thinner of course.
Mike
----- Original Message -----
From: "Lee Whiteman" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, January 10, 2001 2:30 PM
Subject: Re: [TN] Spray fluxing
> Ioan,
>
> Here's an input from my colleague, Art Kramer:
>
> The concern with specific gravity of the flux is diminished with
spray
> fluxing assuming the spray reservoir is airtight. Without the
agitation of
> foam fluxing the flux solvents will not volatize and the specific
gravity
> should remain relatively constant. It is always a good idea however
to
> regularly monitor the specific gravity but not nearly as often as
with a
> foam flux system. It is imperative to regulate and adjust as
necessary the
> amount of flux applied and the direction of the spray nozzles. Once
properly
> adjusted there should be a uniform application of flux over the
entire
> underside of the assembly. Also ensure proper adjustment of any air
knives
> used to remove excess flux. However if the spray fluxer is properly
set-up
> there should be very little need for air knives. Finally,
maintenance with a
> spray flux system is essential to good operation. Ensure the spray
nozzles
> are flushed thoroughly after each use. This is essential if you are
using a
> water soluble flux because the higher solids content will clog the
spray
> nozzles if allowed to dry. Although it may seem that spray fluxing
is more
> difficult to set-up, the advantages are worth the additional effort.
Spray
> fluxing yields more consistent application and also aids in top-side
wetting
> due to the increased penetration of flux into plated thru holes.
>
> Good Luck
>
> Lee Whiteman
> Senior Manufacturing Engineer
> ACI / EMPF
> Telephone: (610) 362-1200; Ext. 208
> FAX: (610) 362-1290
> E-Mail: [log in to unmask] <mailto:[log in to unmask]>
>
>
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]]On Behalf Of Tempea, Ioan
> > Sent: Tuesday, January 09, 2001 1:18 PM
> > To: [log in to unmask]
> > Subject: [TN] Spray fluxing
> >
> >
> > Hi again Technos,
> >
> > and a Happy New Year.
> >
> > Badly need some information on the principles of setting up spray
> > fluxing in
> > our wave soldering process. The main problem I have is that, with
the foam
> > fluxer, the target was clear, a certain specific gravity of the
> > flux has to
> > be observed in order to avoid poor soldering and dirty boards.
> >
> > Now, what do I have to monitor with the spray fluxer?
> >
> > Thanks,
> > Ioan
> >
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